1. Field of the Invention
The present invention relates to a scanning optical system manufacturing method, and a beam inspection method and an beam inspection apparatus.
2. Description of the Related Art
Conventionally, spot diameter measurement has been performed as a part of optical performance evaluation of an image-forming optical system or a scanning optical system including the image-forming optical system. Generally, since an enlarged spot diameter reduces a peak light quantity of a beam spot, a printed image has a tendency of providing a low density at an image height having an enlarged spot diameter. Since it is not possible to ship such a product that produces density unevenness remarkably degrading image quality, an image-forming optical system or a scanning optical system involving an large spot diameter, even if it is local, is disposed of or re-adjusted before an assembly stage of an image forming apparatus.
Japanese Patent Application Laid-Open No. 2002-086795 discusses a method for evaluating a spot diameter in which the light quantity distribution of a spot is analyzed while a two-dimensional area light-receiving sensor is moving in the scanning direction.
However, since a relation between the spot diameter and the image density is not linear, some printed images have no problem even if the spot diameter exceeds an inspection value, and other printed images have density unevenness even if the spot diameter does not exceed the inspection value. In a production site, just a nondefective/defective determination is more important than identifying a cause, and further an evaluation apparatus enabling shortening measurement time and simplifying apparatus configuration is required. On the other hand, the method for measuring a spot diameter has a problem that measurement takes time.